JP5934318B2 - Method for measuring the thermal stability of proteins in milk powder - Google Patents

Description

  The present invention relates to a dairy product processing area, and more particularly, to a method for measuring the thermal stability of proteins in milk powder.

  Milk drinks are made from raw milk or dairy products and processed either fermented or unfermented, and have abundant nutritional components and unique flavors. Has been. However, the production amount of raw milk is limited depending on the region where the dairy cows are raised, and the freshness retention period of the raw milk product is short, so it is necessary to process the product as soon as possible to produce the product. As a result, dairy processing companies that are not in raw milk production areas generally employ dairy products such as whole milk powder and skim milk powder as raw materials for milk beverages. As described above, a product produced from whole milk powder or skim milk powder and prepared by ultra high temperature sterilization (UHT) treatment is referred to as a concentrated reduced milk product.

  Concentrated and reduced dairy products, when UHT treatment is performed during the processing process, the protein in the raw milk powder is not easily denatured under high temperature conditions, forms a precipitate, and interacts with mineral substances to create a blade or pipe for sterilization equipment. Plaque builds up on the line and the internal pressure of the sterilization equipment system increases as the heated surface builds up, and if the internal pressure of the system reaches a certain level, the heat transfer during the sterilization process is affected. As a result, the heat treatment efficiency is lowered, the protein index in the final product is lowered, the deterioration is caused by the mass growth of microorganisms, the production is stopped for a while, and the sterilization equipment must be subjected to intermediate cleaning (AIC). When using powdered milk with excellent protein heat stability as a raw material, the sterilization facility can be operated continuously for at least 6 hours. When milk powder having low protein heat stability is used as a raw material, sterilization equipment generally has to operate for 1.5 to 5 hours and then perform AIC. That is, if milk products are produced using milk powder having low protein thermal stability, the production cost is increased. Therefore, the protein thermal stability of milk powder directly affects the continuous operation time, AIC frequency and production cost of sterilization equipment.

  In actual production, the protein thermal stability of different brands or different batches of milk powder is different. Therefore, by selecting powdered milk with excellent protein heat stability from different brands or different batches of powdered milk, performing corresponding production, extending continuous operation time, and reducing the frequency of AIC, Reducing costs is an urgent need for dairy processing companies. There is no special provision for protein thermal stability in Taiwan's current dairy national standards, and a method for speedily measuring protein thermal stability in milk powder has not been published for a while. For this reason, it is important to provide a method for quickly and accurately measuring the thermal stability of proteins in milk powder.

  The present invention provides a method for measuring the thermal stability of proteins in milk powder. The measuring device used in this measuring method is simple, inexpensive to manufacture, and can measure the thermal stability of protein in milk powder quickly and accurately, reducing the cost of intermediate washing and improving production efficiency. Can do.

  In order to achieve the above object, the present invention provides the following technical solutions.

The present invention provides a method for measuring the thermal stability of proteins in milk powder, which comprises the following steps.
Step A: Powdered milk is mixed with water to obtain a first sample solution.
Step B: Take the first sample solution, seal it in a stainless steel device, pre-heat it for 5-10 minutes under the condition of 50-90 ° C., and heat-treat it under the condition of 120-150 ° C. for 5-15 minutes, Cool and centrifuge to obtain a second sample solution.
Step C: Based on the volume of the first sample solution and the second sample solution, the solid content of the milk powder is obtained. That is, the solid content of milk powder = (volume of the first sample solution−volume of the second sample solution) / volume of the first sample solution · 100%.
If the solid content of the milk powder is lower than 2.00%, the heat stability of the protein is excellent.
If the solid content of the milk powder is 2.00% or more and lower than 3.68%, the heat stability of the protein is normal.
If the solid content of the milk powder is 3.68% or more, the protein thermal stability is low.

  The measurement method provided by the present invention uses a specially designed stainless steel tube and accurately simulates the process of ultra-high temperature sterilization, thereby accurately measuring the thermal stability of protein in milk powder.

  In order to guarantee the accuracy of the measurement result, it is preferable to use a first sample solution having a protein content of 3% to 7%.

  Stainless steel materials are used for the blades and pipes of the ultra-high temperature sterilizer, and in order to accurately simulate the working conditions of the ultra-high temperature sterilization equipment, the stainless steel equipment is used in the present invention to concentrate concentrated reduced dairy products. Is heat-treated. In one embodiment provided by the present invention, the stainless steel device is a stainless steel tube.

  In one embodiment provided by the present invention, the stainless steel tubing is a specially designed stainless steel tubing. Stainless steel tubing includes stainless steel pipes, silicon packing, stainless steel washers, and stainless steel threaded sealing caps.

  When performing ultra-high temperature sterilization, the presence of gas can have a negative effect on the processing of dairy products, so in actual production a degassing process must be performed. In one embodiment provided by the present invention, in step B, the first sample solution is taken and sealed in a stainless steel device so that the ultra-high temperature sterilization process is accurately simulated and the measurement results are closer to actual production. When doing so, fill the tube so that there are no voids in it.

  Preferably, the heating medium for the high temperature treatment in Step B is a fluid having a boiling point of 300 ° C. or higher and does not generate smoke or scorch even under high temperature heating conditions.

  In an embodiment provided by the present invention, the heating medium for the high temperature treatment in Step B is dimethyl silicone oil.

  In order to ensure that the milk powder is sufficiently dissolved in water to obtain concentrated reduced milk, the temperature of the water used for preparing the first sample solution in Step A is preferably 50 to 70 ° C.

  In order to guarantee product quality and reduce the occurrence of stains, when producing concentrated reduced dairy products in actual production, it is better to use deionized water as the water to be used, and the ultra-high temperature sterilization process is accurate In an embodiment provided by the present invention, the water for preparing the first sample solution is deionized water in order to simulate the measurement results closer to actual production.

  In order to ensure that the milk powder is sufficiently dissolved in water to obtain concentrated reduced milk, in one embodiment provided by the present invention, the mixing in step A is performed under conditions of 50-70 ° C., 300-500 rpm / min. Stir for 8-12 minutes.

  In an embodiment provided by the present invention, the cooling in Step B is performed by using a preliminarily heat-treated and high-temperature-treated first sample solution, specifically, by using 15 to 25 ° C. flowing water. Cool to ° C.

  Centrifugation is required to separate the protein precipitate. In an embodiment provided by the present invention, the centrifugation in step B is performed for 4 to 6 minutes under conditions of a relative centrifugal force of 140 to 180 kg.

  In one embodiment provided by the present invention, the milk powder is selected from whole milk powder or skim milk powder.

  The present invention provides a kind of method for measuring the thermal stability of proteins in milk powder. The method includes the following steps. That is, the step of mixing milk powder with water to obtain a first sample solution, taking the first sample solution, sealing it in a stainless steel device, pre-heat treating it at 50 to 90 ° C. for 5 to 10 minutes, 120 to 150 A step of obtaining a second sample solution by high-temperature treatment for 5 to 15 minutes under the condition of ° C, cooling and centrifuging, and obtaining a solid content of the milk powder based on the volume of the first sample solution and the second sample solution . That is, the solid content of milk powder = (volume of the first sample solution−volume of the second sample solution) / volume of the first sample solution · 100%. If the solid content of the milk powder is lower than 2.00%, the heat stability of the protein is excellent. If the solid content of the milk powder is 2.00% or higher and lower than 3.68%, the heat stability of the protein is high. If the solid content of the milk powder is 3.68% or more, the protein heat stability is assumed to be low.

  By using the measurement method provided by the present invention, it is possible to accurately measure the thermal stability of the protein of the milk powder standard product, and the heat stability of the protein in the milk powder standard product measured by the measurement method provided by the present invention. Gender is consistent with reality. That is, the milk powder that is considered to have excellent protein thermal stability according to the measurement method provided by the present invention has a continuous operation time of 7.54 hours in the ultra-high temperature sterilization facility, and the measurement method provided by the present invention. Milk powder with low protein heat stability has a continuous operation time of only 4.57 hours in the ultra-high temperature sterilization facility, and such results are measured using the measurement method provided by the present invention. The thermal stability of the protein in the milk matches the actual production, and the existing measurement technology cannot accurately measure the thermal stability of the protein in milk powder, and the practicality of the existing measurement technology in the actual production is compared Low. As can be seen, the measuring equipment of the measuring method provided by the present invention is simple, low in production cost, speedily and accurately measures the thermal stability of proteins in milk powder, reduces the cost of intermediate washing, and produces Efficiency can be increased.

  The present invention discloses a kind of method for measuring the thermal stability of proteins in milk powder. Anyone who has ordinary knowledge in this technical field can appropriately change the process parameters based on the content of the text. In particular, it should be stated that all similar exchanges or modifications, which are clearly easy for those with ordinary knowledge in the art, are considered to belong to the present invention. . The methods and applications of the present invention have been described with reference to preferred embodiments and are described in the text without departing from the content, spirit and scope of the present invention by those having ordinary skill in the art. The technique of the present invention can be realized and applied by improving or appropriately changing and combining the above and applications.

  Milk powder and apparatus used in the method for measuring the thermal stability of protein in milk powder of the present invention are both commercially available. Among them, as for the stainless steel pipe material, a commercially available product may be purchased, and the literature (SOMMER, HHAND HART, EB The heat coagulation of milk. J. Biol. Chem., 40: 137-151.1919.) Is referred to. May be designed.

  The present invention will be described in more detail below by combining examples.

  Example 1 It is a measurement of the heat stability of protein in a whole milk powder standard product.

  Three types of standard milk powders with known protein heat stability are selected, of which standard A is excellent in protein heat stability, standard B is normal in protein heat stability, and standard C Is a protein with low thermal stability. As a result of measuring the protein content in these standard products, the protein content in these three standard products was 25%. Weigh 30 g of each of the above standard products, weigh 220 g of 50 ° C. water, slowly add the weighed standard product at 300 rpm / min using an IKA stirrer and stir for 12 minutes. Are completely dissolved, and a first sample solution A, a first sample solution B, and a first sample solution C each having a protein content of 3% are obtained. Among them, the first sample solution A is obtained from the standard product A, the first sample solution B is obtained from the standard product B, and the first sample solution C is obtained from the standard product C.

The first sample solution A, the first sample solution B, and the first sample solution C are put into a stainless steel pipe, respectively, filled with the inside of the stainless steel pipe, without generating voids, and provided with a silicone packing, a stainless steel washer, and a stainless threaded sealing cap. Attach the stainless steel tube in a sealed state, and install it twice. Use commercially available stainless steel tubing. The above-mentioned stainless steel tube loaded with the first sample solution A, the first sample solution B, and the first sample solution C is placed in a heating facility at 50 ° C., pre-heated for 10 minutes, taken out, and then in a constant temperature facility. The heating medium of the thermostatic equipment is dimethyl silicone oil, the set temperature is 120 ° C., and the high temperature treatment time is 15 minutes. After the heating is finished, the high-temperature treated stainless steel pipe material is quickly taken out, and the temperature of the stainless steel pipe material is quickly lowered to 15 ° C. with flowing water at 15 ° C. Open the stainless steel screw seal cap of the stainless steel tube, inject the sample solution after the above treatment into the precipitation tube, perform quantitative centrifugation at 160 g for 6 minutes, take the supernatant of the upper layer, and make another precipitate. Put it in a tube, perform quantitative centrifugation again at 160 g for 6 minutes, take the supernatant liquid of the upper layer, obtain the second sample solution A, the second sample solution B, and the second sample solution C, respectively, and quantify it The solid content = (volume of the first sample solution−volume of the second sample solution) / volume of the first sample solution · 100%, and the results are shown in Table 1.

  As can be seen from the test results described above, the average value of the solid content of the standard product A is 1.00%, which is lower than 2.00%, and the thermal stability of the protein is excellent in the measurement method provided by the present invention. Is measured, and the measurement result agrees with the actual.

  The average value of the solid content of the standard product B is 2.20%, which is between 2.00% and 3.68%, and the thermal stability of the protein is normal in the measurement method provided by the present invention. Is measured, and the measurement result agrees with the actual.

  The average value of the solid content of the standard product C is 4.02%, which is higher than 3.68%, and it is measured by the measurement method provided by the present invention that the thermal stability of the protein is low. Match.

  As can be seen, the measurement method provided by the present invention can accurately measure the thermal stability of the protein in the whole milk powder.

  Example 2 It is a heat stability measurement of the protein in skim milk powder standard goods.

  Three types of non-fat dry milk standard products with known protein thermal stability are selected, of which standard D is excellent in protein thermal stability, standard E is normal in protein thermal stability, and standard F is The protein has low thermal stability. As a result of measuring the protein content in these standard products, the protein content in these three standard products was 32%. Weigh each 28g standard product, weigh 100g of 70 ° C water, slowly add the measured standard product to water at 500rpm / min using IKA stirrer and stir for 8 minutes. Are completely dissolved, and a first sample solution D, a first sample solution E, and a first sample solution F each having a protein content of 7% are obtained. Among them, the first sample solution D is obtained from the standard product D, the first sample solution E is obtained from the standard product E, and the first sample solution F is obtained from the standard product F.

The first sample solution D, the first sample solution E, and the first sample solution F are put into a stainless steel pipe, respectively, to maintain a full state, without generating voids therein, a silicone packing, a stainless steel washer, and a stainless steel screw. Attach the combined sealing cap in order, and the stainless steel tube material is sealed, and it will be installed twice. The stainless steel pipe used is designed with reference to the literature (SOMMER, HHAND HART, EB The heat coagulation of milk. J. Biol. Chem., 40: 137-151.1919.). The stainless steel tube loaded with the first sample solution D, the first sample solution E, and the first sample solution F is put in a heating facility at 90 ° C., pre-heated for 5 minutes, taken out, and then placed in a constant temperature facility. The heating medium of the thermostatic equipment is dimethyl silicone oil, the set temperature is 150 ° C., and the high temperature treatment time is 5 minutes. After the heating is finished, the high-temperature treated stainless steel pipe material is quickly taken out, and the temperature of the stainless steel pipe material is quickly lowered to 25 ° C. with flowing water at 25 ° C. Open the stainless steel screw seal cap of the stainless steel tube, inject the sample solution after the above treatment into the precipitation tube, perform quantitative centrifugation at 180 g for 4 minutes, take the supernatant of the upper layer, and make another precipitate. Place in a tube, perform 180g of quantitative centrifugation again for 4 minutes, take the supernatant liquid of the upper layer, obtain second sample solution D, second sample solution E, and second sample solution F, respectively, and quantify it The solid content = (volume of the first sample solution−volume of the second sample solution) / volume of the first sample solution · 100%, and the results are shown in Table 2.

  As can be seen from the above test results, the average value of the solid ratio of the standard product D is 0.86%, which is lower than 2.00%, and the thermal stability of the protein is excellent in the measurement method provided by the present invention. Measurement results are consistent with the actual results.

  The average solid content of the standard product E is 2.47%, which is between 2.00% and 3.68%, and that the thermal stability of the protein is normal in the measurement method provided by the present invention. Is measured, and the measurement result agrees with the actual.

  The average value of the solid content of the standard product F is 3.88%, which is higher than 3.68%. The measurement method provided by the present invention measured that the protein has low thermal stability. Match.

  As can be seen, the measurement method provided by the present invention can accurately measure the thermal stability of the protein in skim milk powder.

  Example 3 It is a measurement of the thermal stability of protein in a whole milk powder standard product.

  Three different types of full-fat milk powder of different brands were selected, and the protein content was measured as brand G, brand H, and brand I. The results were as follows for brand G, brand H, and brand I whole milk powder. They were 25%, 24.8% and 24.5%, respectively. Weigh 50 g of brand G whole fat milk powder, weigh out 200 g of 70 ° C. water, slowly add the weighed brand G whole milk powder milk to water at 400 rpm / min using an IKA stirrer for 10 minutes. After stirring and completely dissolving, a first sample solution G having a protein content of 5% was obtained. Weigh 50 g of brand H whole fat milk powder, weigh 198 g of 70 ° C. water, slowly add the weighed brand H whole milk powder at 400 rpm / min to water using IKA stirrer for 10 minutes. After stirring and completely dissolving, a first sample solution H having a protein content of 5% was obtained. Weigh 50 g of brand I whole milk powder, weigh 195 g of 70 ° C. water, slowly add the weighed brand I whole milk powder to water at 400 rpm / min using IKA stirrer for 10 minutes. After stirring and completely dissolving, a first sample solution I having a protein content of 5% was obtained.

  The first sample solution G, the first sample solution H, and the first sample solution brand I are put into the stainless steel pipes, respectively, so that the full state is maintained so as not to generate voids therein, the silicone packing, the stainless steel washer, The stainless steel threaded sealing cap is attached in order, and the stainless steel tube material is sealed and installed twice. The stainless steel pipe used is designed with reference to the literature (SOMMER, H.H. AND HART, E.B. The heat coagulation of milk. J. Biol. Chem., 40: 137-151.1919.). The stainless steel tube loaded with the first sample solution G, the first sample solution H, and the first sample solution I is put in a heating facility at 70 ° C., pre-heated for 8 minutes, taken out, and then put into a constant temperature facility. The heating medium of the thermostatic equipment is dimethyl silicone oil, the set temperature is 135 ° C., and the high temperature treatment time is 10 minutes. After the heating is finished, the high-temperature treated stainless steel pipe material is quickly taken out, and the temperature of the stainless steel pipe material is rapidly lowered to 20 ° C. with flowing water at 20 ° C. Open the stainless steel threaded sealing cap of the stainless steel tube, inject the sample solution after the above treatment into the precipitation tube, perform quantitative centrifugation at 160 g for 5 minutes, take the supernatant of the upper layer, and make another precipitate. Place in a tube and perform centrifugation again at 160 g for 5 minutes, and remove the supernatant liquid from the upper layer to obtain the second sample solution G, the second sample solution H, and the second sample solution I, respectively. The solid content = (volume of the first sample solution−volume of the second sample solution) / volume of the first sample solution · 100%, and the results are shown in Table 3.

In actual production, the ultra-high temperature sterilization equipment continuous operation time can directly reflect the thermal stability of proteins in milk powder. If the ultra-high temperature sterilization equipment continuous operation time exceeds 6 hours, it can be determined that the thermal stability of the protein in the milk powder of this batch is excellent. If the ultra-high temperature sterilization equipment continuous operation time is 4 to 6 hours, it can be determined that the thermal stability of the protein in the milk powder of this batch is normal. If the ultra-high temperature sterilization equipment continuous operation time is 4 hours or less, it can be determined that the thermal stability of the protein in the milk powder of this batch is low. The above-mentioned three different brands (brand G, brand H, brand I) whole milk powder are used to produce concentrated reduced milk with a protein content of 2.3%. When the sterilization operation was continuously performed, the steam valve was fully opened, and the sterilization temperature did not reach 138 ° C., the continuous operation time was recorded for the ultra-high temperature sterilization equipment, and the results are shown in Table 3.

  As can be seen from the above test results, the average solid content of brand G is 1.16%, and it is said that the protein has excellent thermal stability as measured by the measurement method provided by the present invention. The continuous operation time of the sterilization facility is 7.54 hours.

  The average solid content of brand H is 1.92%, and it is considered that the thermal stability of the protein is excellent as measured by the measuring method provided by the present invention. .08 hours.

  The average solid content of Brand I is 3.68%, and the protein has low thermal stability as measured by the measurement method provided by the present invention. The continuous operation time of the ultra-high temperature sterilization facility is 4.57. It's time.

  As can be seen, the measurement method provided by the present invention can accurately measure the thermal stability of proteins in whole milk powder.

  Contrast 1 Measures the thermal stability of proteins in a whole milk powder standard.

  About the whole fat milk powder of three types of brands in Example 3 (brand G, brand H, brand I), the heat stability of the protein is measured by a well-known measurement method.

  The specific measurement method is as follows. First, the protein content in the whole milk powder of three types of brands (brand G, brand H, brand I) was measured. As a result, the protein content in the whole milk powder of these three types of brands was 25%. Weigh out 80g of each of the above whole milk powders, weigh out 320g of 50 ° C water, slowly add the weighed standard product at 400rpm / min using IKA stirrer, dissolve completely, A whole milk powder solution having a protein content of 5% is obtained. The whole milk powder solution is hydrated for 10 minutes under the condition of 400 rpm / min. 100 g each of the whole milk powder solution is put into three 250 mL serum bottles, and the caps are screwed together to produce three parallel whole milk powder solutions. The parameters of the experimental high-temperature high-pressure sterilization pan are set at 90 ° C. for 45 minutes, and the model number of the high-temperature high-pressure sterilization pan is STURDYsa-300vl. Three parallel whole milk powder solutions are treated at 90 ° C. for 45 minutes in a high temperature autoclave. When the high-temperature and high-pressure sterilization pan is cooled to 70 ° C. or lower, the serum bottle is taken out, and the whole milk powder solution is sucked up with a 10 mL sterilized syringe, and slowly dropped into a metering cylinder containing 500 mL of water. The measurement criteria are as follows. After the whole milk powder solution is treated at high temperature and high pressure, it is dropped into a measuring tube containing 500 mL of water with a syringe, and if the whole milk powder solution is rapidly and uniformly dispersed in water, the heat stability of the protein Is excellent. If the whole milk powder is uniformly dispersed in water and a small granular condensate visible to the naked eye is suspended in it, the heat stability of the protein is normal. It is assumed that the heat stability of the protein is relatively low if the whole milk powder solution generates a relatively severe aggregation phenomenon and is difficult to be dripped with a syringe, and the aggregate rapidly settles in water at the time of dropping. If a cloud-like lump appears in the whole milk powder solution and cannot be dispersed when dripped in water, and the cloud-like lump quickly settles to the bottom of the water, the protein has low thermal stability.

  According to the measurement results, high-temperature and high-pressure treatment of three types of branded milk (brand G, brand H, brand I) was performed and then dropped into a measuring cylinder containing 500 mL of water with a syringe. All of the milk powder solutions were rapidly dispersed in water, and it was found that all of the protein heat stability of brand G, brand H, and brand I whole milk powder measured by the above-described measurement method was excellent.

  However, in actual production, when brand G is used to produce concentrated reduced milk with a protein content of 2.3%, the continuous operation time of the ultra-high temperature sterilization equipment is 7.54 hours continuous operation. When using H to produce concentrated reduced milk with a protein content of 2.3%, the ultra-high temperature sterilization facility has a continuous operation time of 6.08 hours, and using brand I, the protein content is 2 When producing 3% concentrated reduced milk, the continuous operation time of the ultra-high temperature sterilization facility is 4.57 hours. From this, it can be seen that there is a certain difference in the solid content of the three types of whole milk powder, and there is also a certain difference in the thermal stability of the proteins in the three types of whole milk powder. It is inferred.

  As can be seen from the above, the above-described well-known measurement methods cannot accurately measure the thermal stability of proteins in milk powder, and their practicality during actual production is relatively low.

  The foregoing is only a description of the preferred embodiment of the present invention, and is not intended to limit the present invention. Other equivalent effect modifications or substitutions that may be accomplished without departing from the spirit of the present invention are not Are also within the scope of the claims of the present invention.

Claims (10)

A method for measuring protein thermal stability in milk powder,
Mixing milk powder with water to obtain a first sample solution; and
Take the first sample solution, seal it in a stainless steel device, pre-heat it for 5 to 10 minutes under the condition of 50 to 90 ° C., heat it for 5 to 15 minutes under the condition of 120 to 150 ° C., cool and centrifuge Step B separating to obtain a second sample solution;
Obtaining a solid content of the milk powder based on the volume of the first sample solution and the second sample solution, and
Solid content of the above milk powder = (volume of the first sample solution−volume of the second sample solution) / volume of the first sample solution · 100%,
If the solid content of the powdered milk is lower than 2.00%, the protein thermal stability is excellent,
If the above-mentioned milk powder has a solid content of 2.00% or more and lower than 3.68%, the protein heat stability is normal,
A method for measuring protein thermal stability in milk powder, wherein the protein thermal stability is low when the solid content of the powdered milk is 3.68% or more.   The method for measuring protein thermal stability in milk powder according to claim 1, wherein the first sample solution has a protein content of 3% to 7%.   The method for measuring protein thermal stability in milk powder according to claim 1, wherein the stainless steel device is a stainless steel tube material.   4. The method for measuring protein thermal stability in milk powder according to claim 3, wherein the stainless steel tube material includes a stainless steel pipe, a silicon packing, a stainless steel washer, and a stainless steel threaded sealing cap.   The protein in milk powder according to claim 1, wherein the heating medium for the high temperature treatment described above is a fluid that has a boiling point of 300 ° C or higher and does not generate smoke or scorch even under continuous high temperature heating conditions. Measurement method of thermal stability.   The method for measuring protein thermal stability in milk powder according to claim 1, wherein the temperature of the water in step A is 50 to 70 ° C.   In step A, the above-mentioned mixing is performed for 8 to 12 minutes under the conditions of 50 to 70 ° C and 300 to 500 rpm / min. The heat stability of protein in milk powder according to claim 1, Measuring method.   2. The method for measuring protein thermal stability in milk powder according to claim 1, wherein in the step B, the cooling is performed to 15 to 25 ° C. using flowing water at 15 to 25 ° C. 3. The measurement of protein thermal stability in milk powder according to claim 1, characterized in that, in step B, the centrifugation is performed for 4 to 6 minutes under conditions of a relative centrifugal force of 140 to 180 g. Method.   The method for measuring protein thermal stability in milk powder according to claim 1, wherein the milk powder is selected from whole milk powder or skim milk powder.